Nearly 50% of U.S. veterans report they experience pain on a regular basis. This chronic pain often co-occurs with other disorders including PTSD, depression, anxiety and insomnia. A common approach to treating chronic pain is opioid analgesics, which are not always effective, and increasingly associated with abuse and misuse. Thus, there is an urgent need to develop readily available, safe, and practical complementary non-pharmacological approaches to manage chronic pain in U.S. veterans. Chronic pain is a multidimensional phenomenon, inter-related with many factors, including negative mood and poor sleep. The central circadian clock, in the suprachiasmatic nucleus in the hypothalamus, is well recognized to regulate both mood and sleep, and even small delays (shifts later) in circadian/sleep timing are associated with depression and disrupted sleep. These results suggests that later circadian/sleep timing may be a modifiable risk factor for pain. Our pilot data suggest that: (1) later circadian/sleep timing is associated with worse anger, depression, anxiety, fatigue and physical function; (2) a self-administered home based bright light treatment is effective at shifting circadian phase. Thus, self-administered bright light treatment at home may be a potentially efficacious adjunctive strategy for managing chronic pain. This R34 proposal will develop a morning bright light treatment to help manage chronic pain and improve PTSD symptoms, depression, anxiety and sleep in U.S. veterans. Patients will have 7 baseline days at home, followed by a baseline pain sensitivity assessment and home circadian phase assessment (dim light melatonin onset). Following an instructional home visit, patients will then self- administer morning bright light treatment for 6 days, followed by reassessments of pain sensitivity and circadian phase. Assessments will be repeated after another 7 days of morning bright light treatment. Pain, mood and sleep (wrist actigraphy) will be assessed daily throughout baseline and treatment. Pain, mood and sleep will also be rated by veterans daily during a 1 month follow up after cessation of light treatment. Aim 1 is to determine the feasibility and acceptability of bright light treatment in a sample of U.S. veterans (n=30) experiencing chronic low back pain. Aim 2 is to examine the effects of 6 days and 13 days of bright light treatment on their chronic pain intensity and sensitivity (improved PTSD symptoms, mood and sleep are secondary outcomes) to reveal the treatment duration needed to affect an adequate pain reduction response. Aim 3 is to determine the time course of decay of treatment response after cessation of light treatment to gain information for the development of a maintenance bright light treatment (e.g. bright light every second or third day). Long-term significance of this project addresses the need to develop readily available, safe, and practical approaches to manage chronic pain in U.S. veterans not exclusively based on analgesic medications. More immediately, the project will examine important parameters surrounding the implementation of an effective course of bright light treatment to provide an important foundation for a future clinical trial.